Second Fin Ray Shows Promise For Estimating Ages Of Juvenile But Not Adult Lake Sturgeon

The first marginal pectoral fin ray (fin spine) is the most common structure used for estimating the age of sturgeons, including Lake Sturgeon Acipenser fulvescens. However, conflicting results from studies on the effects of fin spine removal have made some managers hesitant about the practice. We investigated whether the second pectoral fin ray, which can be removed in a less invasive procedure, could be used for estimating ages of Lake Sturgeon. Ages estimated from fin spine and second fin ray samples were compared for 53 wild (470 to 1,981 mm TL) and 16 stocked, known-age (ages 8-18) Lake Sturgeon. Mean coefficient of variation for all samples was 12.4% for the fin spine and 17.5% for the second fin ray. In known-age fish, 17% of estimated ages for the fin spine and the second fin ray matched true age. For the remaining estimates, the difference between the second fin ray and true age was greater than the difference between the fin spine and true age (P < 0.05, Wilcoxon's signed rank test). In juvenile fish (n = 24), 75% of ages estimated from fin spines and second fin rays were within +/- 4 annuli, which was similar to differences in reader agreement for the same fin spine. Age estimates for adult Lake Sturgeon (n = 45) were less when using the second fin ray relative to the fin spine (up to -34 years). Additionally, poor annulus clarity was observed in >70% of the second fin rays sampled from adult fish. Our results suggest that the second fin ray does not provide reliable age estimates for adult Lake Sturgeon but may have some utility for estimating age of juvenile Lake Sturgeon. Additional research with a larger sample size would be required to provide more conclusive results.